This invention pertains to a polymer composite lace which can be used in the place of natural rawhide laces. The lace can be used in a wide variety of applications, in particular in the use of sporting goods.
Rawhide laces are traditionally used in a number of sports equipment applications, including baseball gloves and footwear such as hiking boots. While rawhide is relatively inexpensive, it is subject to wide variability in strength and suppleness. Defects in rawhide laces often go undetected until the lace separates in use. Further, the laces may stiffen when exposed to water and allowed to dry.
Various attempts have been made to manufacture synthetic laces which can simulate the strength and feel of natural rawhide. These designs generally have involved reinforcing an extruded thermoplastic lace by embedding synthetic cords in the thermoplastic matrix. Various surface treatments and pigments can be used to simulate the patina of leather. While these laces have found application in the craft and ornamentation industries, they have been found to be unsuitable for sporting applications. When the laces are flexed, and particularly when they are repeatedly flexed and bent through sharp angles as in tying a tight, compact knot, the synthetic cords tend to cut through the thermoplastic matrix and emerge at the surface (the xe2x80x9ccheesecutterxe2x80x9d effect). This type of failure is illustrated in FIG. 1 of the drawing. Because of this effect, prior art laces can only be used in applications where they will not be bent through sharp angles or flexed repeatedly.
A need therefore still exists for a synthetic rawhide lace which can be repeatedly flexed and tied, and which exhibits a greater uniformity and reliability than natural rawhide.
In one aspect, the invention comprises a strip of artificial leather comprising at least one reinforcing cord encased in a matrix, where the cord remains encased in the matrix when the strip is subjected to a migration test by pulling over a xc2xcxe2x80x3 at a load of at least 4500 pounds per square inch of cross-sectional area of the strip (4.5 ksi). In a related aspect, the invention comprises a strip of artificial leather comprising at least one reinforcing cord encased in a matrix, where the cord remains encased when the strip is subjected to a migration test by pulling to its breaking strength. In both of these embodiments, the matrix comprises poly(vinyl chloride) and either nitrile rubber or urethane. The reinforcing cord or cords may be made, for example, of polyester. The combined strength of all cords may be at least 8000 pounds per square inch of cross-sectional area of the strip. The matrix may incorporate additives such as fibers, particles, flock, leather dust, hydrocarbon resins, and plasticizers. The outer surface of the strip may be embossed or given an appearance of leather. The flex modulus of the strip may be matched to that of rawhide. The strip may be sufficiently strong and flexible that a tight, compact knot can be tied in the strip without migration of the reinforcing cords to the surface of the strip.
In another aspect, the invention comprises methods of making artificial leather strips. These methods include extruding matrix material around cords (e.g., polyester cords), or coextruding a thermoplastic reinforcing filament with the matrix. The matrix material comprises poly(vinyl chloride) and nitrile rubber or urethane. The reinforcing elements may remain encased in the matrix when the strip is subjected to a migration test using a force greater than 4500 pounds per square inch of cross-sectional area of the strip, or using a force equal to the breaking force of the strip.